A vortex tube is a device which separates an incoming compressed gas into cold and hot streams. The experimental results reported by various researchers were used as a database to obtain a correlation. A term called Rutika-Ramakrishna Correlation Factor or RR Correlation Factor is coined which correlates the parameters such as ratio of length of the vortex tube to the diameter of the vortex tube, ratio of diameter of central orifice to the diameter of the vortex tube and Reynolds number of flow in the vortex tube to the maximum isentropic efficiency of the vortex tube. Experiments to validate the legitimacy of RR Correlation Factor were conducted with air as the working medium using different types of vortex tubes. The cold end temperature of the vortex tube as obtained by experiments is slightly lower than the values estimated using RR Correlation Factor. Thus, this correlation factor (RR) can be used as a powerful tool to design a vortex tube. © 2020 Elsevier Inc.